Proportional solenoids position an armature axially within a housing as a function of applied current or voltage. Ideally, the armature can move to infinitely variable positions corresponding accurately to infinite variations in the applied voltage or current. To accomplish this in practice, though, requires that the armature move with very low friction within the housing, and achieving this has made proportional solenoids expensive.
The housing, the armature, and sometimes bearings arranged between the armature and the housing all have to be machined accurately for the sliding axial fit of the armature within the housing to have minimal friction. Diameters and concentricity of bearing surfaces must be highly accurate to minimize friction, and location and shape of bearing surfaces must be considered to minimize effects of side or off-axis loading. These needs have required that all contacting surfaces be accurately machined, and errors that inevitably occur in attempting to accomplish this adversely affect solenoid performance.
The machining accuracy that is required to keep friction low in proportional solenoids increases their price sufficiently so that some users who could benefit from proportional solenoids avoid them in favor of simpler and lower cost non-proportional solenoids, even though performance is less than optimum. Our invention aims at reducing the cost of making proportional solenoids accurate enough to minimize friction.